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CVE-2026-48489 – Security Firewall Bypass / Authentication Bypass – Symfony (all branches prior t…

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Summary

CVE-2026-48489 is a high-severity security firewall bypass vulnerability in the symfony/security-http component of the Symfony PHP framework. When a firewall is configured with failure_forward: true, an unauthenticated attacker can craft a failing login request to bypass access_control rules and receive the response from a protected route as if they were authenticated. The vulnerability carries a CVSS 4.0 base score of 8.7 (Critical).

Technical details

  • Root cause: DefaultAuthenticationFailureHandler reads the attacker-controlled _failure_path request parameter when failure_forward: true is enabled, and uses its value as the target path for an internal subrequest dispatched via HttpKernelInterface::SUB_REQUEST.
  • Trigger condition: A firewall must be configured with form-login (or any authenticator backed by DefaultAuthenticationFailureHandler) with the failure_forward: true option set. This is a non-default configuration.
  • Why the bypass works: Symfony’s Firewall::onKernelRequest listener intentionally skips subrequests on the assumption they are internally generated and trusted. As a result, AccessListener — which evaluates access_control rules — never executes for the subrequest. The attacker effectively reaches a protected GET route outside the firewall perimeter.
  • Attack vector: An unauthenticated attacker sends a POST to the login check path with a crafted _failure_path parameter (e.g., _failure_path=/admin/protected-resource) and receives the controller response for the targeted route without any credentials.
  • Impact: Unauthorized read access to access_control-protected GET endpoints — including data exports, internal APIs, and administrative views — constitutes a significant authentication bypass and information disclosure. No privileges, user interaction, or prior knowledge of application internals are required beyond a valid login endpoint. Classified as CWE-863 (Incorrect Authorization).

Affected software

  • symfony/security-http (and symfony/symfony) — all versions prior to 5.4.53
  • symfony/security-http (and symfony/symfony) — versions 6.0.0 through 6.4.40 (prior to 6.4.41)
  • symfony/security-http (and symfony/symfony) — versions 7.0.0 through 7.4.12 (prior to 7.4.13)
  • symfony/security-http (and symfony/symfony) — versions 8.0.0 through 8.0.12 (prior to 8.0.13)

Severity

CVSS 4.0 base score: 8.7
Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N

Mitigation and recommended actions

  • Immediate — apply the vendor patch: Upgrade to one of the fixed releases that corresponds to your active branch:
    • 5.4.53
    • 6.4.41
    • 7.4.13
    • 8.0.13
  • If immediate upgrade is not feasible — configuration workaround: Disable the failure_forward: true option in your security.yaml firewall configuration and revert to the default redirect-on-failure behavior (failure_forward: false). This eliminates the subrequest code path exploited by this vulnerability.
  • Audit scope: Review all Symfony firewall configurations for the presence of failure_forward: true to determine whether your deployment is in the vulnerable configuration.

IONIX Status

The IONIX research team is tracking ongoing exploitation attempts and recommends immediate patching. Potentially affected assets are outlined in this post.

References

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